PURPOSE: To reduce the loss of a refrigerant by conducting a heater by a heater energizer only for a period when the reverse voltage of a superconducting coil is small at excitation or demagnetization and stopping conduction to the heater for a period when reverse voltage is large and the heater has sufficient self-heat generation.
CONSTITUTION: The heater energizer 22 introduces the output voltage Vs of an absolute-value circuit 21 and the output voltage V1 of a reference-voltage generator 23 into a comparator 24, and transmits output X only for the period of V1>Vs from the comparator 24. The output X of the comparator 24 is given as the ON control signals of a second switching circuit 26 interposed into a heater energizing circuit through a first switching circuit 25. The first switching circuit 25 is ON-OFF controlled by the output signals of a controller 27. When set signals S are transmitted from the outside, the controller 27 starts the transmission of ON control signals P, and stops the transmission of said ON control signals P at a point of time when the output X of said comparator 24 rises twice and the output Vs of said absolute-value circuit 21 reaches zero.
HEKI TOSHIKI
MITSUNE SUSUMU
MOROHOSHI KOUKI
MATSUDA MASAHARU
TOKYO SHIBAURA ELECTRIC CO